fdisk(ADM) 19 June 1992 fdisk(ADM) Name fdisk - maintain disk partitions Syntax /etc/fdisk [ [-p ] [ -ad partition ] [ -c partition start size ] [ -t ostype ]] [ -f devicename ] [ -f devicename ] ] Description fdisk displays information about disk partitions. It also creates and deletes disk partitions and changes the active partition. fdisk func- tionality is a superset of the MS-DOS command of the same name. fdisk is usually used interactively from a menu. The hard disk has a maximum of four partitions. Only one partition is active at any given time. It is possible to assign a different operating system to each partition. Once a partition is made active, the operating system resident in that partition boots automatically once the current operating system is halted. The fdisk utility reports disk sizes in tracks. The number of tracks available on a hard disk is equal to the number of heads times the number of cylinders. The fdisk utility does not allocate the first track or the last cylinder on the hard disk when the ``Use Entire Disk for UNIX'' option is used. The first track on the hard disk is reserved for master- boot and the last cylinder is generally used when running hard disk diag- nostics. You should not allocate the last cylinder if you plan to run diagnostics on your hard disk. For example, if a disk has 4 heads and 615 cylinders, it has 2460 tracks, which fdisk reports as tracks 0-2459. If you choose the ``Use Entire Disk for UNIX'' option, fdisk will create a UNIX partition on tracks 1- 2455. Track 0 is reserved for masterboot, and the last cylinder (tracks 2455-2459) is not assigned with the ``Use Entire Disk for UNIX'' option. Partitions are defined by a ``partition table'' at the end of the master boot block. The partition table provides the location and size of the partitions on the disk. The partition table also defines the active par- tition. Each partition can be assigned to the UNIX system, DOS, or some other operating system. Once a DOS partition is set up, DOS files and directories resident in the DOS partition may be accessed from the UNIX system partition by means of the dos(C) commands. DOS may be booted without the DOS partition being active by entering dos at the boot prompt. See boot(HW). Arguments -p, -a, -d,-c These flags are used to invoke fdisk non-interactively. The argument number, below, refers to a valid partition number (1-4). -p Prints out the disk partition table, one partition to a line. For each partition, fdisk displays the following information: partition start stop size status type -a number Activates partition number. -d number Deletes partition number. -c number start size Creates a partition number that is size tracks long beginning at track start. The -c option is used to use the entire disk for UNIX; the appending of a dash (-) to the end of the command line accomplishes this, as in the following example: fdisk -c 1 1 - This syntax is used only during installation. If there are any existing partitions on the disk, this command will fail. -f name Open device name and read the partition table associated with that device's partition. The default is /dev/rhd00. -t ostype Specify the partition type of the partition being creat- ed, where ostype is one of the following: UNIX, XENIX, DOS, DOS_12, DOS_16, DOS_32, OS/2 or CCPM. DOS is the same as DOS_16. If no -t option is specified, the default partition type is UNIX. Options When invoked interactively (without the -p, -a, -d, or -c options), fdisk displays a prompt and a menu of five options. No changes are made to the partition table on the disk until you enter ``q'' from the main menu. 1. Display Partition Table This option displays a table of information about each partition on the hard disk. The ``PARTITION'' column gives the partition number. The ``STATUS'' column tells whether the partition is active (A) or inactive (I). ``TYPE'' tells whether the partition is a UNIX system partition, a DOS partition, or ``other''. The option also displays the starting track, ending track and total number of tracks in each partition. 2. Use Entire Disk for UNIX fdisk creates one partition that includes all the tracks on the disk, except the first track and the last cylinder. This partition is assigned to the UNIX system and is designated the active partition. 3. Use Rest of Disk for UNIX fdisk creates one partition that occupies the largest available con- tiguous area of the disk. This partition is assigned to the UNIX sys- tem and is designated the active partition. 4. Create UNIX Partition This option allows the creation of a partition by altering the parti- tion table. fdisk reports the number of tracks available for each partition and the number of tracks in use. fdisk prompts for the par- tition to create, the starting track and size in tracks. The change is written to the hard disk when you enter ``q'' from the main menu. 5. Activate Partition This option activates the specified partition. Only one partition may be active at a time. The change is not effective until you exit. The operating system residing in the newly activated partition boots once the current operating system is halted. 6. Delete Partition This option requests which partition you wish to delete. fdisk reports the new available amount of disk space in tracks. The change is not effective until you exit. Exit the fdisk program by typing a ``q'' at the main fdisk menu. Your changes are now written to the hard disk. Notes The minimum recommended size for a UNIX system partition is 40 megabytes. Since fdisk is intended for use with DOS, it may not work with all oper- ating system combinations. OS/2 partitions are displayed as UNKNOWN. See also dos(C), hd(HW) Value added fdisk is an extension of AT&T System V provided by The Santa Cruz Opera- tion, Inc.